Influence of pH on the growth and leaf-maceration ability of fungi involved in the decomposition of floating leaves of Nymphaea alba in an acid water

Abstract

Summary: Ten species of fungi were isolated from floating leaves cut from plants of Nymphaea alba in various initial stages of decay, which were collected from an acidic moorland pool. None of the fungal species isolated belonged to the aquatic Hyphomycetes sensu Ingold or the aero-aquatic fungi sensu Van Beverwijk. Growth experiments were conducted with five of the species on media containing glucose, polysaccharide or isolated cell walls of N. alba, each at three pH values. The fungi investigated were capable of growth on a variety of structural polysaccharides, indicating their potential importance in leaf degradation. Low pH inhibited growth on media containing glucose, pectin or cell wall fraction. Utilization of carboxymethylcellulose and crystalline cellulose did not differ much within the pH range studied. The fungi isolated were grown on N. alba leaf strips at three pH values to study the influence of pH on leaf maceration. All the fungi investigated could develop at low pH (4·0), but maceration was only observed at pH 5·5 or 7·5. It is likely that inhibition of pectin degradation is an important factor causing suppression of leaf fragmentation at low pH. This may contribute to the inhibition of the decomposition of macrophyte remains in acid aquatic systems.